The present invention relates to clutches in general, and more particularly to improvements in clutch assemblies which can be utilized with advantage in the power trains of motor vehicles to transmit torque between a prime mover (such as an internal combustion engine, an electric motor or a hybrid drive) and a gearbox or transmission. Still more particularly, the invention relates to improvements in clutch assemblies which receive torque from the rotary output element of a prime mover (e.g., from the crankshaft or from the camshaft of an internal combustion engine) and can be operated to transmit torque to discrete first and second rotary input elements (e.g., to coaxial first and second shafts) of a gearbox.
The invention also relates to methods of assembling and operating clutch assemblies of the above outlined character.
It is already known to transmit torque between the prime mover of a motor vehicle and the gearbox in the power train of the vehicle by resorting to two friction clutches. Each clutch can be actuated by the operator of the vehicle by way of a discrete pedal or automatically by way of a control unit. A drawback of conventional arrangements of such character is that the operating point of a friction clutch is shifted in response to wear in actual use of the friction clutches; this necessitates a change in the magnitude of the actuating force which must be applied in order to engage or disengage the clutches. This exerts a negative influence upon the operation of the clutches as well as upon their actuation.
An object of the instant invention is to provide a novel and improved multiple clutch assembly which can be utilized with particular advantage in the power trains of motor vehicles.
Another object of the present invention is to provide a clutch assembly wherein the clutches cooperate in a novel and improved manner.
A further object of this invention is to provide novel and improved friction clutches which can be utilized in the above outlined multiple clutch assembly.
An additional object of the invention is to provide a power train, particularly for use in motor vehicles, which employs a clutch assembly of the above outlined character.
Still another object of our invention is to provide a motor vehicle which embodies a power train employing the above outlined clutch assembly.
A further object of the present invention is to provide a relatively simple and inexpensive multiple clutch assembly which can be utilized as a superior substitute for presently known multiple clutch assemblies.
Another object of our invention is to provide a clutch assembly whose operation remains at least substantially unchanged during the useful life of the arrangement, such as the power train of a motor vehicle, wherein the clutch assembly is put to use.
An additional object of the invention is to provide a clutch assembly wherein the individual clutches can be engaged and disengaged in a highly reliable and unchanging manner during the entire useful life of the assembly.
Still another object of the present invention is to provide a novel and improved method of operating the above outlined clutch assembly.
A further object of the invention is to provide a method which renders it possible to automatically compensate for and to avoid the adverse effects of unequal wear upon the individual clutches of the above outlined clutch assembly.
Another object of the invention is to provide a clutch assembly which can be fully or practically fully assembled in the manufacturing plant rather than at the locale of installation into the power train of a motor vehicle or any other arrangement in which the clutch assembly is being put to use.
Still another object of the invention is to provide novel and improved controls for clutch assemblies of the above outlined character, for their clutches, for the prime movers which transmit torque to the clutches and/or for the devices (such as automatically shiftable gearboxes) which receive torque from the individual clutches of the clutch assembly.
A further object of the invention is to provide a novel and improved gearbox which can be combined with the above outlined clutch assembly.
One feature of the present invention resides in the provision of a clutch assembly which comprises a rotary input member connectable with a rotary output element of a prime mover (e.g., with the crankshaft or camshaft of an internal combustion engine in the power train of a motor vehicle), a housing which is rotatable with the input member, first and second input elements which are coaxial with the output element (such input elements can constitute interfitted input shafts of a change-speed transmission or gearbox in the power train of the motor vehicle), first and second clutch discs which are respectively rotatable with the first and second input elements and have first and second friction linings which are subject to wear in actual use of the clutch assembly, a first pressure plate which is connected with the output element (preferably by way of the input member), a first counterpressure plate connected with the housing in such a way that the first friction lining(s) is or are disposed between the first pressure plate and the first counterpressure plate, a second pressure plate which is rotatable with the housing, a second counterpressure plate rotatable: with the input member and installed in or relative to the housing in such a way that the second friction lining(s) is or are disposed between the second pressure plate and the second counterpressure plate (the second counterpressure plate is or can be installed in such a way that it is disposed between the second clutch disc and a portion of the housing), and adjusting means having means for compensating for wear upon at least one of the first and second friction linings (particularly for compensating for unequal wear upon the first and second friction linings).
The first counterpressure plate has or can have limited freedom of axial movement relative to the housing, and the second counterpressure plate has or can also have limited freedom of axial movement relative to the housing.
The first pressure plate, the first counterpressure plate and the first clutch disc constitute component parts of a first friction clutch which is or can be connected in parallel with a second friction clutch including the second pressure plate, the second counterpressure plate and the second clutch disc. Such clutch assembly preferably further includes automated means for actuating the first and second friction clutches, and the two friction clutches can form part of a twin clutch. The clutch assembly can further comprise first and second actuating means for the respective friction clutches. At least one of the actuating means can include a diaphragm spring (Belleville spring) or a membrane. If at least one of the actuating means includes a diaphragm spring, such spring is preferably arranged to normally maintain the respective friction clutch in at least partially engaged condition; the diaphragm spring is deformable to thus allow for disengagement of the respective friction clutch.
One of the actuating means can include a (first) portion which bears upon one of the counterpressure plates, and such clutch assembly can further comprise an annular distancing element which is interposed between a second portion of the one actuating means and the other actuating means, The first or second portion of the one actuating means is or can be more distant from the common axis of the friction clutches than the second or first portion of the one actuating means. The distancing element can include first and second ring-shaped portions having different diameters and respectively abutting the first and second actuating means of the clutch assembly. It is often desirable that the diameter of the first ring-shaped portion exceed the diameter of the second ring-shaped portion of the distancing element.
The second actuating means can include a first portion which bears upon the respective counterpressure plate, and the clutch assembly can further comprise a function element and an annular intermediate part which is interposed between the function element and a second portion of the second actuating means. The latter is tiltable relative to the intermediate part and the function element can include or constitute a diaphragm spring or a membrane.
At least one of the actuating means can comprise an elastically deformable annular base (such as a ring-shaped washer-like part) and actuating portions (such as prongs or tines) extending radially inwardly from the base.
The clutch assembly further comprises first and second drives which preferably engage the radially inner portions of the respective (first and second) actuating means. The actuating means have first sides which confront and second sides which face away from the respective clutch discs, and the drives are preferably adjacent the second sides of the respective actuating means.
The second actuating means has a first portion which bears upon the respective counterpressure plate and the aforementioned intermediate part is preferably interposed between the function element and a second portion of the second actuating means. The latter is tiltable relative to the intermediate part. The function element can comprise or constitute a diaphragm spring or a membrane having an axially fixed radially inner portion which abuts and is tiltable relative to the housing. Such clutch assembly preferably further comprises a fulcrum for the second actuating means and the fulcrum is installed between a radially outer portion of the function element and the second actuating means.
The function element can form part of the adjusting means and the latter is or can be arranged to ensure the application of at least substantially constant forces to the counterpressure plates through the medium of the first and second actuating elements.
A portion of the function element can constitute a bearing for the second actuating means and such bearing is movable axially of the output element in dependency upon the extent of wear upon at least one of the friction linings.
The aforementioned compensating means can include means for compensating for wear upon the first and second friction linings.
The aforementioned intermediate part can include or constitute an annulus which is interposed between the function element and a portion of the second actuating means. At least one of the actuating means is operable to generate a force which opposes a second (supporting) force generated in response to the bias of a bearing acting upon the second actuating means. The bearing can form part of the function element.
It is also within the purview of the present invention to configurate and install the actuating means in such a way that one thereof can generate a force developing in response to wear upon at least one of the friction linings. The force is applied to the function element and increases in response to increasing wear upon the friction linings. The just mentioned force exceeds an opposing force which is generated by the function element. The latter is deformable (such as elastic) so that it can yield when it is subjected to the action of a force being applied by one of the actuating means.
The actuating means can be arranged to apply to the function element a force which increases with increasing wear upon at least one of the friction linings; this results in movement of a portion of the function element in a direction toward the pressure plates. The just mentioned portion of the function element engages the aforementioned intermediate portion or part which is interposed between the function element and one of the actuating means. The force which the actuating means apply to the function element decreases in response to movement of the aforementioned portion of the function element toward the pressure plates. The movement of the aforesaid portion of the function element is terminated upon the establishment of an equilibrium of forces between the forces required for operation of at least one of the actuating means and an opposing force generated by the function element.
Each of the actuating means can have a predetermined range of operation and a downwardly sloping characteristic curve which slopes downwardly at least within a portion of the respective range.
The second actuating means can include a (first) portion which bears upon the respective counterpressure plate. The aforementioned preferably annular intermediate part is or can be interposed between the function element and a second portion of the second actuating means. The latter is tiltable relative to the intermediate part and the function element (e.g., a diaphragm spring or a membrane) can be arranged to store energy for the generation of a force which is at least substantially constant within the contemplated range of compensation for wear by the adjusting means.
The function element (which can constitute a membrane or a diaphragm spring) is or can be mounted to yield axially of the clutch assembly and can constitute a bearing for a portion of one of the actuating means; the bearing is stressed in a direction toward the housing of the clutch assembly.
The automatic wear compensating device of the clutch assembly can be installed between the housing and one of the actuating means. The wear compensating device can include a portion one side of which faces one of the actuating devices; such portion of the wear compensating device is movable axially of the output element toward the pressure plates and is arranged to be arrested against movement away from the pressure plates.
A portion of the wear compensating device can be interposed between the clutch housing and the first actuating means. Such portion of the wear compensating device can be arranged to adjust a spring-biased mobile resilient seat for one of the actuating means to an extent corresponding to the extent of movement of at least one of the actuating means as a result of wear upon at least one of the friction linings.
The wear compensating means can include a ring-shaped member which is urged by at least one of the actuating means axially of the output element, at least during absence of actuation of the respective friction clutch.
The aforementioned automatic wear compensating device can include at least one adjusting ramp which slopes in the axial direction of the output element. The at least one ramp can be provided on an annular member of the automatic wear compensating device; such annular member can be provided with or can carry an annular member. The automatic wear compensating device further comprises at least one second ramp which cooperates with the at least one adjusting ramp. The at least one second ramp can be provided on a ring which is disposed between the housing and the annular member. The at least one ramp can slope at an angle of between 5 and 20 degrees, preferably at an angle of between about 8 and 12 degrees. The ramps frictionally engage each other and have slopes at angles which prevent self-locking by friction. Means can be provided to bias the aforementioned ring toward the aforementioned annular member and/or vice versa.
The aforementioned automatic wear compensating device can act as a freewheel in the direction of disengagement of at least one of the friction clutches but the device is preferably self-locking in the opposite direction.
In a presently preferred embodiment of the improved clutch assembly, the automatic wear compensating device includes at least one mobile adjusting portion.
The automatic wear compensating device can be arranged to carry out wear compensation as a function of changes of RPM of at least one rotary part of the improved clutch assembly and/or to be deactivated at at least one predetermined speed of the at least one rotary part of the clutch assembly; such device can be blocked at rotational speeds of the at least one rotary part above 1000 RPM.
If the output element constitutes the output element (such as a camshaft or a crankshaft) of a prime mover (such as an internal combustion engine) in the power train of a motor vehicle, the automatic wear compensating device can be arranged to be operative at RPMs of the output element during idling and at RPMs below the idling RPM of the prime mover.
The arrangement can be such that the automatic wear compensating device is activatable at substantially zero RPM of a rotary part of the power train.
The automatic wear compensating device can include a first support for at least one first ramp, a second support for at least one second ramp which abuts and is movable relative to the first ramp (and/or vice versa) in the axial direction of the output element, and means (such as one or more coil springs, diaphragm springs or the like) for biasing one of the supports toward the other support. The biasing means can be arranged to turn the one support relative to the other support.
The aforementioned function element can constitute a bearing for one of the actuating means.
At least one of the friction linings can include a first section, a second section and resilient means between such sections. One of the sections can be frictionally engaged by the respective pressure plate, and the other section can be engaged by the respective counterpressure plate. The resilient means can have a distance-force characteristic which at least approximates the distance-force characteristic of the force being exerted by the first and second actuating means upon the respective pressure plates.
Another feature of the present invention resides in the provision of a method of actuating an assembly which comprises a plurality of clutch discs having friction linings which are subject to wear, for example, when utilized in the power train of a motor vehicle to transmit torque from a rotary output element (such as a camshaft or a crankshaft) of a prime mover (such as an internal combustion engine or a hybrid drive) to discrete input elements of a gearbox, and wherein the wear upon the friction linings is compensated for by adjusting means. The method comprises the steps of monitoring the extent of wear upon at least one of the friction linings, and influencing the extent of wear upon at least one of the friction linings when the monitored extent of wear exceeds a preselected value.
The influencing step can include altering the extent of wear upon at least one of the friction linings in order to ensure that the wear upon any one of the friction linings at least approximates the extent of wear upon each other friction lining.
The monitoring step can include at least representatively ascertaining the extent of wear upon the at least one friction lining. The ascertaining step can include determining the extent of wear upon each of the friction linings.
At least in many or most instances, the ascertaining step can include measuring the extent of wear upon the at least one friction lining.
The ascertaining step can also include calculating the extent of wear upon the at least one friction lining, and such calculating step can include determining the extent of wear upon the at least one friction lining on the basis of calculated energy input of the respective friction clutch. Each clutch includes a clutch disc which is disposed between a pressure plate and a counterpressure plate. At least one of the friction clutches is operable with slip in the partly engaged condition thereof, and the aforementioned energy input is a function of the RPM of the clutch including the at least one friction lining during operation with slip. The calculated energy input is or can be a function at least of friction torque of the respective friction clutch or at least of a coefficient of wear. The latter can be a function of temperature, such as the temperature of at least one of the friction clutches. This method can further comprise the step of monitoring the temperature of the at least one friction clutch, e.g., with a temperature model.
The calculating step of the improved method can include ascertaining the extent of wear upon the friction linings by way of statistical evaluation of parameters of characteristic curves. The parameters can pertain to the measuring points of the respective friction clutches. At least one of the parameters can pertain or relate to the maximum friction torque of one of the friction clutches.
Alternatively, at least one of the parameters can relate to the maximum actuating force of one of the friction clutches. The calculation of actuating force of at least one of the friction clutches is or can be dependent at least upon the maximal speed of an actuator for the at least one friction clutch. The maximum actuating force of the at least one friction clutch can depend at least upon the work of the actuator for the at least one friction clutch.
The arrangement can be such that the ascertaining step is not appreciably affected by short-lasting influences. The calculation of a new value is or can be effected iteratively on the basis of an actual value and a predetermined value with attendant weighting of the respective values. The calculation of a new value can involve an averaging of several previously ascertained values.
The method can further comprise the steps of comparing the values which serve as a basis for the calculating step with reference values, and utilizing the results of the comparing step to establish a function which is at least representative of the extent of wear upon at least one of the friction linings.
The influencing step of the improved method can include adjusting the clutch assembly of at least two friction clutches when the averaged values of individual values of the extent of wear upon the at least one friction lining reach a preselected value. Such method can further include the step of actualizing (if necessary) at least some of the reference values upon completion of the adjusting step and as a function of the characteristics of the friction clutch including the at least one friction lining.
The monitoring step of the method can include ascertaining the extent of wear upon each of the friction linings, and such method can further comprise the step of comparing the extents of wear upon the friction linings prior to the influencing step. Still further, such method can comprise the step of memorizing the results of the comparing step. Moreover, the said influencing step of such method can include altering the wear upon at least one of the friction linings when the comparing step indicates a predetermined difference between the extents of wear upon the friction linings.
The altering step of the just discussed method can include at least one of (a) increasing the extent of wear upon the friction lining which has undergone less wear, and (b) reducing the extent of wear upon the friction lining which has undergone more pronounced wear. If the friction clutches including discrete friction linings serve to transmit torque in the power train of a motor vehicle (such as between the rotary output element of the prime mover and discrete input shafts of a multispeed gearbox or transmission), the transmission of torque by the clutches is or can be varied in dependency upon the extent of wear to which the respective friction linings are subjected. Some speeds of the gearbox are associated with each of the friction clutches, and such method can further comprise the step of shifting the gearbox into a speed associated with that friction clutch which is to vary the transmission of torque in dependency upon the extent of wear upon the respective friction lining.
The output element of the prime mover in the power train which includes the just discussed clutch assembly is rotatable at a plurality of different speeds, and the method can include the additional step of increasing the extent of engagement of at least one of the friction clutches in response to increasing speed of the output element. Such additional step preferably includes increasing the extents of engagement of the friction clutches at different rates in response to increasing speed of the output element of the prime mover. The additional step can include increasing the extent of engagement of the at least one friction clutch at a rate which is dependent upon the position of a multiple-position load lever for the friction clutches with weighting factors corresponding to the extent of wear upon the friction linings.
The altering step of the method can further include at least temporarily operating with slip that one of the clutches the friction lining of which has undergone less pronounced wear, and disengaging that friction clutch the lining of which has undergone more pronounced wear.
The altering step of the improved method can further include at least temporarily operating with slip that one of the friction clutches the friction lining of which has undergone less pronounced wear and at least temporarily operating without slip that friction clutch the friction lining of which has undergone more pronounced wear.
It is also within the purview of the invention to resort to a method according to which the altering step further includes engaging that friction clutch the friction lining of which has undergone less pronounced wear, particularly during coasting of the motor vehicle. If the gearbox in the power train embodying the clutch assembly has a plurality of different speeds or ratios (e.g., five forward speeds, a neutral position and at least one reverse speed) some of which are associated with a first friction clutch and the others of which are associated with at least one second friction clutch, the influencing step can include shifting the gearbox into a higher speed associated with the clutch the friction lining of which has undergone less pronounced wear. Such method can include the additional step of increasing, in response to the application of a vehicle brake, the extent of torque transmission by that friction clutch the friction lining of which has undergone less pronounced wear.
A further feature of our present invention resides in the provision of a method of reducing the likelihood of damage to an automatically operable clutch assembly including a plurality of friction clutches with friction linings which undergo wear in actual use of the clutch assembly, particularly in the power train of a motor vehicle which further comprises means for compensating for wear upon the friction linings. The method comprises a first step of ascertaining the extent of wear upon the friction linings as a result of unintentional slip of the clutch (e.g., a slip which causes wear that adversely influences the useful life and/or the predictability of operation of the clutch assembly), and a second step of carrying out undertakings to at least reduce the extent of unintentional additional slip of the clutch, namely one of several clutches which constitute the clutch assembly.
The second step can include limiting the extent of energy input to the clutch assembly in response to unintentional slip of at least one of the friction clutches. Such limiting step can include throttling at least one of the variables including (a) the transmission of torque by the prime mover which is connected with the clutch assembly in the power train of a motor vehicle, and (b) the RPM of a rotary element of the prime mover.
Alternatively, or in addition to the aforediscussed undertakings, the limiting step can include limiting the extent of slip of the friction clutches which form part of the clutch assembly.
Still another feature of the present invention resides in the provision of a clutch assembly which comprises a rotary input member connectable with a rotary output element of a prime mover, a housing which is rotatable with the input member, first and second rotary input elements coaxial with the output element, and first and second friction clutches each of which includes a pressure plate, a counterpressure plate and a clutch disc disposed between the two plates and having friction linings which are subject to wear in actual use of the respective clutch. The clutch discs of the first and second friction clutches are respectively rotatable with the first and second input elements, the pressure plate of the first clutch is connected to the output element and the counterpressure plate of the first clutch is connected with the housing. The pressure plate of the second friction clutch is rotatable with the housing and the counterpressure plate of the second clutch is rotatable with the input member and is disposed between the clutch disc of the second clutch and the housing. The clutch assembly further comprises control means for automatically actuating the friction clutches and means for at least reducing the likelihood of damage to the friction clutches. Such likelihood reducing means includes means for compensating for wear upon at least one of the first and second friction linings.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The iproved clutch assembly itself, however, both as to its construction and the modes of assembling, installing and operating the same, together with numerous additional important and advantageous features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.